ABSTRACT
A novel multilayer cap, employed in an enhancement-mode Si-doped AlGaAs/InGaAs/Si-doped AlGaAs FET, has been investigated for 3.5V highly efficient power amplifier applications. The multilayer cap, consisting of Si-doped GaAs cap/undoped-GaAs/Si-doped AlGaAs, was designed to reduce contact resistance(Rc) between the cap and the channel. Rc reduction of 0.05 ω·mm was achieved. As a result, a 0.5μm gate length FET exhibited a low on-resistance of 1.6 μ·mm and a maximum drain current of 390mA/mm with a gate-to-drain breakdown voltage of 17V. Under single 3.5V operation at 950MHz, a high power-added efficiency of 65.5% was obtained at the PDC output criteria for the 24mm gate width FET.
